The present invention relates to a semiconductor photolithography technique, and more particularly, to a photolithography mask and method for manufacturing the mask which can be used to form a fine pattern on a semiconductor substrate.
Generally, it is well known that various semiconductor patterns can be formed by photolithography. Photolithography can largely be divided into two steps.
First, a photoresist whose solubility is changed by exposure to, for example, ultraviolet, X-ray or electron beam radiation, is coated on an insulating film or a conductive film formed on a semiconductor substrate, i.e., on a film wherein a pattern is to be formed. A predetermined portion of the photoresist is exposed to light using a mask, and the portion having a high solubility is removed by a development process, to thereby form a photoresist pattern.
Second, an exposed portion of film is removed by an etching process, to thereby form various kinds of patterns such as wiring or electrodes.
Recently, photolithography has become an important process in the production of semiconductor devices having a high packing density. Typically, a semiconductor device repeatedly goes through the process of serially forming and patterning a plurality of films on a semiconductor substrate. As the manufacturing procedure has developed, high packing density of the semiconductor device can be achieved when the fine pattern is formed on a stepped structure.
FIG. 1 shows a method for forming a pattern by the conventional method.
When an ultraviolet or an electron beam 1 is irradiated onto a mask 2 having a mask pattern, the mask pattern is projected via a projection lens 3 of a stepper onto a photoresist formed on a semiconductor wafer 9 having a stepped portion 110. At this time, the part of the photoresist formed on the top of stepped portion 110 is sufficiently exposed (reference numeral 4 denotes an unexposed photoresist portion and 5 denotes an exposed photoresist portion), whereas the photoresist portion 6 formed over the wafer 9 is under-exposed. The resulting photoresist pattern is shown in (B) of FIG. 1. The part of the photoresist formed over the stepped portion 110 is much thinner than that formed over the wafer regions which are below the stepped portion 110, when a photoresist is coated onto the semiconductor wafer 9 having stepped portion 110. Thus, when the photoresist is exposed, the photoresist formed on the wafer regions at the bottom of stepped portion 110 is insufficiently exposed. Therefore, the resulting photoresist at the bottom of stepped portion 110 has a "bridge" between patterns where exposure is insufficient at reference numeral 6, thereby making it difficult to form an exact pattern.
To overcome this problem, a multi-layer resist (MLR) method has been proposed.
FIG. 2 shows a method for forming a fine pattern using the MLR method.
Specifically, a lower photoresist layer 20 is coated on a semiconductor wafer 26 having a stepped structure 110, and an upper photoresist is coated on an insulating material layer 22, (e.g., an oxide film) disposed between the upper and lower photoresist layers. Then, a light 1 is irradiated onto the semiconductor wafer using mask 2 and projection lens 3, so that the upper photoresist layer can be exposed as shown in (A) of FIG. 2 (reference numeral 24 is an unexposed portion of the upper photoresist, reference numeral 25 is an exposed portion of the upper photoresist). Then, the upper photoresist is developed to form an upper photoresist pattern 24a as shown in (B). Then, as shown in (C) of FIG. 2, the insulating material layer 22 is anisotropically etched using the upper photoresist pattern 24a as an etching mask, to thereby form an insulating pattern 22a. Lower photoresist 20 is anisotropically etched, to thereby form a lower photoresist pattern 20a.
When a fine pattern is formed on a semiconductor wafer having a stepped structure using, the MLR method, only the upper photoresist is formed, exposed and developed, and the insulating material layer 22 and the lower photoresist 20 are anisotropically etched using the developed upper photoresist as an etching mask, to thereby form a pattern. Therefore, a photoresist residue cannot be generated on the semiconductor wafer at the bottom of stepped structure 110.
However, the MLR method is too complicated and productivity is poor, which increases cost. In addition, anisotropic etching can result in defects.